WASTE DISPOSAL IN LANDFILL

WASTE – A MOUNTING PROBLEM

The risks of not properly controlling waste disposal are:

1. Air pollution

2. Soil contamination

3. Landscape degradation

4. Water pollution via leachate

Our current strategies to managing waste are

1. Isolation by burying waste (also includes containerization and storage)

2. Incineration, diluting or spreading the waste

3. Recycling paper, glass, metals and some plastics

In Britain a massive 111 million tons of waste is buried every year (However in 2014 only 23.1% went to landfill).

The first solid waste landfill site was established in 1912. So how do landfill’s work?

Waste is compacted by heavy machinery

At the end of each day a 15cm thick layer of soil isolates the day’s waste

When the landfill is full, the site is sealed by a layer of soil 50cm thick and the surface graded so water

runs off.

People have the same attitude to landfill sites as they do quarries. No one wants one near their neighborhood but

we all produce waste which must be deposited somewhere. Often, disused quarries and sand, gravel and brick

pits are used. They are seen as ready-made holes in the ground but unfortunately, the geology is rarely ideal for

waste disposal. It is best to site a landfill near to an urban area to reduce the cost and fuel associated with waste

in transit.

Environmental consequences of landfills:

During the activity of the landfill site (tipping), the area is subjected to noise, dust, smells, vermin infestation

and wind-blown litter.

After operations cease:

Biodegradation leads to settling and subsidence which may open cracks and fissures in the site so rainwater

infiltrates waste.

Rainwater percolates through the waste dissolving soluble chemicals and collecting microbial bacteria. The

liquid formed is called leachate and the leachate plume expands laterally in the direction of groundwater flow..

The exact composition varies and it must be considered toxic unless proven otherwise.

Leachate can percolate downward into the surrounding soils and groundwater leading to contamination of

local aquifers and agricultural land.

Additionally, large amounts of methane are

released due to the large amounts of anaerobic

bacteria thriving on the waste during

decomposition. While there is little risk of fires

and explosions due to the anaerobic

environment, the gas must be vented off to

prevent buildup of dangerous levels. Methane is

a greenhouse gas but can be collected and sold

as fuel.

Pollution

plume

Leachates

Impermeable

Problems occur when the underlying rocks are permeable due to joints, bedding planes and faults and the water

table is close to the surface. Contamination by leachates is likely.

Landfill site construction

To reduce the cost of operation, disused quarries or brick pits are used: readymade holes in the ground.

An impermeable base layer is required to prevent toxic leachate percolating out the landfill. Types include

clay, geomembrane linings like HDPE (High Density Polyethylene) and composite.

When the landfill is abandoned, it is sealed with an impermeable cap the same as the base layer used. This is

designed to keep rainwater out so limit the production of leachate. Furthermore, the impermeable cap

deceases the rate of decomposition by limiting water and oxygen.

Surrounding rocks are grouted to prevent leachate leakage.

Leachate may be drained and collected.

Methane gas can be vented or collected and transport by pipelines.

Some more measures to protect the environment

Landfill sites are often covered with a topsoil layer about 50cm thick. This will often dry out and is a major source

of wind-blown dust. Water sprayers are used to limit the dust and aid growth of vegetation.

Unpleasant odours cause complaints among locals. Landfill operators monitor and log complaints. Spraying the

waste with essential oils may help musk the smells.

Vermin such as seagulls and rats are controlled by pest eradicators and birds of prey such as hawks, owls and

falcons.

Windblown litter may be collected using litter fences or mobile collectors on site.

Types of waste for landfills or recycling

1. Biodegradable waste-food, garden materials,

paper

2. Recyclable materials-paper, glass, plastic, cans

3. Inert waste-construction and demolition

materials

Composite waste-clothes, children’s toys, Household

hazardous waste-paint, batteries, light bulbs, bleach,

fertilisers, pesticides and computers.

#Leachate = the fluid generated by water dissolving

soluble chemicals from landfill waste.

#Landfill = disposal of waste where rubbish is buried in

holes within the ground.

Types of waste NOT for landfills

1. Flammable items

2. Reactive or explosive substances

3. Chemicals that are corrosive or toxic

4. Medical waste

5. Radioactive waste

6. Toxic industrial waste & some batteries

7. Tyres

8. Mandatory recyclables

9. Explosives

10. Scrap metal

11. Large appliances (e.g. ovens)

Rock type

Fine grained (<0.0039mm), impermeable rocks such as clays are best suitable for land fill sites and it is

best if they have thick, uniform, flat lying beds.

Porous and permeable rocks such as limestone and sandstone allow flow of leachate so are not suitable

unless covered by an impermeable barrier. Limestone may be dissolved by acidic leachate leading to the

formation of solution cavities. These will destabilize the site.

Crystalline igneous and metamorphic rocks, when not affected by jointing or fracture, are the most

suitable. Weathered rocks decrease stability and also increase permeability and porosity, however, well

cemented sedimentary rocks can prevent leachates.

Geological structures

Faults increase the permeability of rocks and provide escape routes for leachate as do joints in rocks such

as limestone.

Tilted or folded beds allow down-dip and lateral movement of leachate, which can migrate some

distance away from the landfill site through permeable beds.

Anticlines may have some tension joints in their crests.

Groundwater

If the water table is high in relation to the landfill then there is less distance from the leachate to travel

to reach underlying groundwater. The level of water may vary in aquifers.

Control measures to protect groundwater and the environmental engineering practices are very high.

Generally activities such as agriculture and urban areas result in more widespread pollution.

Some landfill sites will only take pre-compacted bails of waste so this limits noise around the site.